This invention relates to the design of hydrofoils and, more particularly, to apparatus for spanning and sealing the gap between the main (or "leading") portion of a hydrofoil and a rearwardly extending, movable flap.
Hydrofoil craft design generally features a hull having downwardly depending struts attached thereto. Hydrofoils are fixed to the lowest ends of the struts and extend substantially orthogonal to them. The hydrofoil itself generally consists of a leading portion and a trailing flap. The leading portion is contoured to provide hydrodynamic lift to the hydrofoil craft as it moves through the water. The flaps, like ailerons of an aircraft wing, are pivotally attached to the trailing edge of the hydrofoil's leading portion and when actuated, control the attitude of the craft as it moves through the water. The flap's leading edge, that is, the portion proximal to the trailing edge of the leading portion of the hydrofoil, is smoothly rounded. The upper and lower surfaces of the flap gradually converge to meet at the flap's trailing edge.
For optimal hydrodynamic performance, it is desirable to provide continuity between the upper and lower surfaces of the leading portion of the hydrofoil and the corresponding upper and lower surfaces of the trailing flap. In this past, the upper and lower surfaces of the leading portion of the hydrofoil were extended to meet in slidable contact with the leading portion of the flap. These surface extensions had to be precisely machined in order to obtain the required hydrodynamic fit, while allowing the necessary operating clearances so that the leading edge of the flap could smoothly turn about the hinge without any binding interaction or undesirably large gaps between the flap and the extended surfaces. In addition to the extensive machining requirements of these surface extensions, the surfaces of the flap also had to be carefully machined to remove any distortions or irregularities that could cause binding as the flap surfaces slide against the surface
In fabricating the conventional hydrofoil and flap, it is important that the axis of rotation of the hinge be located equidistantly from the upper and lower surfaces of the hydrofoil. Thus, for example, if the hinge was improperly mounted so that its axis of rotation was too close to the upper surface of the hydrofoil, rotation of the symmetrically curved leading portions of the flap about the misaligned axis of rotation would create a camming effect, i.e., causing the leading edge of the hydrofoil flap to be forced up against the upper surface extension instead of smoothly sliding against it. Furthermore, even if the axis of rotation of the hinge is properly positioned, another fabrication problem arises in attempting to ensure that the flap is mounted so that the geometric center of its leading portion is aligned with the axis of rotation of the hinge. If the flap is mounted to the hinge slightly off center, the undesirable camming effect will occur.